This invention relates to high-power semiconductor switching power regulators such as are used in propulsion systems of diesel-electric locomotives and the like and, more particularly, to a method and apparatus which provide sufficient cooling capacity and easy installation and maintenance of insulated gate bipolar transistors (IGBT) in such power regulators.
Traction vehicles such as, for example, locomotives, employ electric traction motors for driving wheels of the vehicles. In some of these vehicles, the motors are alternating current (AC) motors whose speed and power are controlled by varying the frequency and current of AC electric power supplied to the motors. Commonly, the electric power is supplied at some point in the vehicle system as direct current power and is thereafter inverted to AC power of controlled frequency and amplitude. The electric power may be derived from an on-board alternator driven by an internal combustion engine or may be obtained from a wayside power source such as a third rail or overhead catenary.
In prior art systems the power is inverted in a solid-state inverter incorporating a plurality of diodes and gate turn-off thyristors (GTO). in a locomotive, large off-highway vehicle, or transit application, the traction motors may develop up to 1000 horsepower per motor thus requiring very high power handling capability by the associated inverter. This, in turn, requires semiconductor switching devices such as GTOs which are capable of controlling such high power and of dissipating significant heat developed in the semiconductor devices due to internal loss generating characteristics.
The semiconductor devices are mounted on heat transfer devices such as heat sinks which aid in transferring heat away from the semiconductor devices and thus preventing thermal failure of the devices. For these very high power semiconductors it is desirable to use heat sinks having generally hollow interiors through which cooling air can be forced to remove accumulated heat. Each heat sink is mounted to an air plenum and cooling air is blown through the heat sinks and in close proximity to the electrical circuit area in which the semiconductors are located. The electrical circuit area may include the various control and timing circuits, including voluminous low power semiconductors, used in controlling switching of the power semiconductors.
In locomotive applications the cooling air is typically derived from blowers drawing air from overhead of the locomotive. The incoming air usually contains contaminants including diesel fumes and dust. A spin filter or inertial filter is used to at least partially clean this cooling air. An inverter for large AC motor applications typically includes six high power GTO devices requiring heat sinks and forced air cooling. Each of these devices are generally press packs which require double side cooling for these high power applications. A common arrangement thus requires twelve heat sinks per inverter. On a six axle locomotive, the inverters alone will include 72 heat sinks requiring cooling air. This number of heat sinks requires a high volume flow of cooling air and concomitant increase in inertial filter capacity. Further, the GTO devices require complex gating circuits and snubber circuits with as many as 250 components to control operation of the devices in a switching mode. Still further, the gating circuits must be of relatively high power since the GTO may require as much as 100 watts for gate control.